There is a growing level of dissatisfaction among consumers and audio professionals alike with extreme variations in the loudness of the audio in radio and television broadcasts and in pre-recorded audio material. Large variations in loudness often occur as listeners tune from one station to another, as the program received from a given station switches between a main feature and commercial advertisements, and as listeners change media in their playback systems such as switching between different compact discs or different DVDs. Listeners are often forced to adjust the volume controls of their receivers and playback systems to maintain a relatively uniform loudness.
One solution that has been proposed to overcome this problem is the use of control information or “metadata” that accompanies the audio information. Metadata, or data that describes the audio data, may be provided in a broadcast or recorded signal to control the playback loudness of the audio information. One example of this type of metadata is described in the Advanced Television Systems Committee (ATSC) A/52A document entitled “Revision A to Digital Audio Compression (AC-3) Standard” published Aug. 20, 2001. This particular standard specifies metadata that includes the parameters, DIALNORM, COMPR and DYNRNG, which pertain to playback signal level and dynamic range. Both signal level and dynamic range affect the perceived or subjective level of a signal, which is referred to as loudness. Receivers that conform to this ATSC audio standard use the DIALNORM parameter to control playback signal levels, and may use the COMPR and DYNRNG parameters to control compression of playback signal dynamic range.
If this type of metadata is used properly during audio content creation, distribution, broadcast and recording processes, the problem with excessive variations in playback loudness could be eliminated or at least greatly reduced. Unfortunately, metadata is sometimes misused or not used at all because it is misunderstood, because the appropriate people do not know how to use it properly, or because it is used to create artistic effects in inappropriate ways.